Meridian Unplugged - Powered by MrTechGuy.co.uk Forums Discussion Meridian - Systems Sorting out Ground Loop problem with Modded Oppo

No, British plugs are keyed but not standard European:
[/quote]

Very strange that one is hot the other neutral yet they don't key them.

Many years ago it was not keyed in the usa but just about everything is now a days.

I doubt flipping polarity will fix his ground loop since he already tried 3 outlets. It never worked for me. Always had to lift a ground.

just to update, Shawn should have replacement SPDIF boards out to me very soon, orders to Waters, Stocker and Powell will ship the day I get them in

sorry for the delays guys, this is out of my hands like many things over the past few months

-Gary

George, i dont know what you mean.
The power line have to have allways a neutral phase and not two hots.
When you measure on your wall outlet both power lines in respect to ground or earth,
what voltages you will get?

You do not have to have one hot and one neutral you can have two "hots".

In the USA hot to neutral is 120v and hot to hot is 220v. 220v means something different in the USA (it means two phases, 2 hots).

Where as in other countries hot to neutral is 220v and I don't believe your residential power has two phases (hot to hot) otherwise I believe it would be 440v.

I didn't realize until I read this thread that 220V is single phase (hot and neutral) in other countries.

So flipping 220V in USA means flipping two hots (it wouldn't do much of anything). Where as in other countries flipping 220V means flipping a hot and neutral which is similar to how it is in the USA for 120V.

Reading this, I have to say that I'd be pretty unhappy about the prospect of messing around with earthing (particularly the dubious suggestion of running an earth from the plug/wall to "a screw" on the rear panel). If it can't be fixed by Gary, it should be returned for a refund IMHO.

Just my tuppence worth.

George

First, thanks for everyone for their input.

Playing around with earthing etc is out of my league in terms of skill and understanding (plus George and Robert lost me a bit).

I have tried what Nutflush suggested and played around with cables etc. No luck. From doing this though it has become apparent that 4 things all need to simultaneously occur for there to be intereference through my speakers:

1. The power amp must be turned on (obvious I suppose, as I would otherwise hear nothing from my speakers hence no noise); and
2. The Oppo is turned on (includes standby mode); and
3. Cables are connected from the Oppo to another piece of kit (any one item, incl TV); and
4. That piece of kit, somehow, has a cabling system that can be traced thru to the power amp. It doesnt matter if that piece of kit is turned on/off or even plugged into a power source.

Point 4. is the important one to note. An example may help to clarify - its a little complicated.

I unplugged all other AV kit from a power source other than the power amp and headphone amp (both in the power board) and the Oppo (direct to wall). All 3 were turned on.

The only audio/video cabling from the Oppo that was plugged into anything else was the analogue outputs, which went into the headphone amp. 2 scenarios then followed.

Scenario 1: The headphone amp also had plugged into another one of its input, the analogue outputs from my Digital TV set top box (e.g. like a Sky HD / cable box).

Scenario 2: Only the Oppo was connected to the headphone amp.

Outcomes: Scenrio 1 = Noise; Scenario 2 = No noise.

I figured that the signal under scenario 1 was making its way back to the power amp via the various cabling. My set top box is also connected to the 568.2mm (via coax digital out), which in turn feeds the power amplifier. So, I figure that the "noise" was going from Oppo, to headphone amp, to Set Top Box, to Meridian, to power amp and finally speakers.

Under Scenario 2, the "noise" had nowhere else to go as nothing else was connected to the headphone amplifier other than my headphones.

* * * * * *

So, in summary, is it fair to say that the Oppo and my power amp just don't like each other? Given I had all other components unplugged, I am assuming it cannot be one of them rather than the power amp.

If it wasn't for Scenario 2 above -- and the fact that via headphones I have no noise -- my conclusion would 100% that the Oppo has issues (maybe it still does anyway? - it is the thing that started it all).

I hope the above is clear. I would appreciate comments on any flaws in my logic and if my noise-routing theory is just bollocks.

Kind regards

Mark,

a few follow up questions:
- did you have an active sub (or any other active speaker = power plug!) connected to your amp? If so: what happens if you disconnect it?
- what was the effect when BOTH amp & Oppo were connected to the SAME power board (including twisting one of the 2 power plugs as a second scenario)?
- do you have a power cord WITHOUT ground (meaning only 2 pins but no other metal parts that connect to any part of the socket)? If so: what is the effect if you try it on the Oppo (or amp)?

Just a little explanation: the "noise" that you hear is a current that is running from one GROUND (i.e. socket 1) to another GROUND (i.e. different wall plug or antenna etc.) passing your amp inbetween (amp is amplifying this current to an audible level and sending it to your speakers for you to enjoy...). That's the reason why simply turning a device off doesn't help (The connection to GROUND is still there. Only the 2 wires from the pins are interrupted, but not the wire to the ground contact.). Only pulling the plug will make a difference.

Although you might think that "GROUND is GROUND = NO CURRENT" there may actually be a voltage difference. So this "noise" is not produced by the Oppo, but rather the result of making a connection between 2 voltage differentials (like the plus & minus sides of a battery). This connection is made by attaching a cable (like the analogue out cables) to the devices (only metal cables count here since an optical connection for example doesn't allow an electrical current to flow). If you connect the 2 devices with a cable that has LESS resistance (i.e. thick cable) the current will take this route and if you are lucky it will NOT pass anything that amplifies it. That's why a (thick) cable connection between the 2 chassis may solve this problem as Gary proposed.

Please let us know how you're going,
Thomas

P.S. More info here: http://www.gbaudio.co.uk/data/ground.htm

Try this scenario again, but unplug your antenna cable from the set top box.

+1

Alternatively use an optical rather than electrical SPDIF connection between your set-top box and processor. I have heard that earth loop hums are the reason why optical is the preferred connection in this scenario.

+1 [/quote]

+1

If this is the cause you can add a balun (to isolate the antenna's ground).

Note: your TV Coax is essentially an antenna in this case.

Explaination http://www.epanorama.net/documents/groundloop/antenna_isolator_building.html

You can buy them for a couple dollars

Thanks again everyone for their suggestions. Some more work tonight/tomorrow night its seems



The sub was not plugged in - in fact, I have not had it plugged in since I got the Oppo.

It is worse when both Oppo and Amp are in the same power board and it is worse when there are just the 2 of them alone (i.e. more components = reduced noise level). I have not tried twisting.

I dont think I have a cord with 2 pins that would fit the 3-pin IEC socket on the amp and Oppo.

I will try an optical connection on the Set Top Box to see if that helps. I have a spare cable. I will also try unplugging the antennae - I did do this last night but don't recall the exact time when I did, but it didn't help.